Spring Fever!
by KiyameHikari-chan
Summary: Gareki has joined the third ship after four years of studying in the city. After his first mission, a sudden attack from a human turned monster called a varuga leads Gareki, Yogi, Tsukumo and Gareki's best friend Nai into a grueling battle. But Nai is acting strange. Why? WARNING: BL BOYS LOVE. Don't like it don't read it. But otherwise enjoy!
1. Chapter 1

**Hey everybody! Just trying out an idea here. I recently watched an anime called Karneval and wanted to try out one of my OTPs from the series. A little background info from the anime, Nai is a man-made boy from experiments mixing a magical creature and human DNA. Gareki is the young man who finds Nai after they both get attacked by a human woman who turns into a monster. They meet up with a crime fighting organization called Circus and are taken into the third ship in the force. That's all I'm going to say for now. If you guys are interested in finding out more I suggest you check out the anime. It's a really good one in my opinion. But that's just me.**

 **Moving on, we shall now kick off our tale of Spring Fever! Hope you guys enjoy this and just fyi it will be a shorter story than my others. Reading START!**

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"Nai?" Gareki called out as he came in through the entrance portal on the ship.

"Welcome back," said one of the robot security lambs on the ship. Gareki gave the greeting that was the code to get in and then went over to a boy with white hair and red eyes. The boy jumped up from the floor happily and dashed towards the taller black haired boy.

"Gareki!" the boy called out happily as he hugged Gareki.

"I'm back. You been good for Yogi and them?"

"Mhmm~," the boy said happily as he ran ahead into the common room.

"Gareki-kun! Welcome back!" Yogi called with his usual annoying smile. Gareki just nodded his head in response and proceeded to remove his jacket.

"So how was your first mission as a Circus member?" Yogi said as the young man took a seat on an empty couch. Nai soon joined him and looked at Gareki in expectation.

"It wasn't all that hard. Once I got used to my assigned weapon during training, varuga aren't much of a problem anymore," Gareki said lightly as he smiled gently at Nai and pet his head. Nai hummed in pleasure and cuddled closer to Gareki in response. Yogi just looked at the pair of friends with mild curiosity.

"Has Nai always done that?"

"Huh?"

"He seems to be acting a little strange today."

"...Strange how?"

"Well this morning he snapped at Tsukumo-chan out of nowhere. And when you let he sat by the entrance the whole time and didn't even come to lunch."

"Nai, you haven't eaten yet?"

Nai looked up at Gareki in confusion.

"I did eat. The sheep brought food."

"Oh! Now I get it. So he did eat. That's a relief...but that doesn't explain why you snapped at Tsukumo-chan this morning."

"She said mean words about Gareki."

"And so you defended my honor. Heheh. See now Yogi, he wasn't acting weird at all."

"I guess not..." _But why is he so close to Gareki-kun? He's clinging much more than usual...but then again Gareki-kun did just join us two days ago after four long years down below. Maybe Nai-kun was really lonely without him..._ Yogi's mind kept running in circles over Nai's behavior just before they got a call to action.

"Gareki, Yogi, Tsukumo, a varuga was spotted in the forest headed towards the city. Get it before it can get any humans," Hirato said as he walked into the room with Tsukumo in tow.

"Hai!" the three said simultaneously as they dashed to the portal. Nai was about to go after them when Hirato pulled him back and dragged him all the way to his and Gareki's room. Nai looked at Hirato in confusion before the man smiled wryly and slammed the door shut. When Nai tried to open the door he found it was locked and he began to panic.

"Hirato open the door," he called as he began to pound into the wood.

"You need to stay here. Nai, you've been acting a bit too oddly so I shall keep you here until they return. Then we will have the doctor look at you. So stay here and calm down for now. I shall return when they start heading ba-"

"Gareki!" Nai shouted suddenly as his overly sensitive ears picked out Gareki's cry of pain. The boy went into panic mode and began to beat the door repeatedly. Hirato tried to brace the door with all his might but a panicked Nai was too strong to deal with. The boy slammed the door open on Hirato, knocking the man unconscious. Nai dashed down the hall to the portal and was instantly transported to the battle field where Gareki lay hurt as Tsukumo and Yogi barely contained a truly insane varuga.

The female varuga turned it's attention to Nai and charged after him. However, Nai managed to dodge her by running slightly faster towards Gareki as his panic continued to grow.

"Gareki!" Nai called out as he slid into a crouch before the young man.

"Nai? What are you doing here?"

"Gareki is hurt!"

As soon as Nai said this, Gareki understood what had happened. _But how the hell did he get out of the bedroom?_ Just as Gareki thought this the varuga launched a new attack, her focus still on Nai. Nai picked up on the varuga and turned a completely malicious glare at it. The varuga stopped in its tracks at the sight of red eyes boiling over with flames of raw anger. The varuga began to back away as Nai stood and approached the monster. Soon it was an all out chase between Nai and the varuga, as he ran the monster right into the trap Yogi and Tsukumo had set. Nai pulled out just in time as vines shot out of the ground and trapped the varuga in place.

Tsukumo delivered the finishing blow by cutting off the monster's head with a well placed blow from one of Yogi's blades. The varuga, having been defeated, vaporized into nothing as Nai turned around and ran back to Gareki.

"Gareki, are you ok?" Nai asked with concern. The young man just looked up and smiled gently at the boy, as he stood up and hugged him. Nai couldn't take it and began to cry in relief over the safety of his friend.

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 **Well this is where I will stop for now. Can't wait to show you guys the rest of the story. But for now adieu! And I look forward to hearing from you guys! Peace! (^o^)V**


	2. Chapter 2

**Konichiwa mina-san(hello everyone)! ((\\(^o^)/)) Man it's been so long since I've been able to get on here. Sorry for my long absence guys. I've been super busy this summer with school and work. I actually didn't have time to do much else besides eat sleep and study so please forgive me. From where we left off last time we have an OC Nai who's super clingy and a different Gareki after he official joins the third ship of Circus as a fighting member. From here on out things get a little more...well you'll see soon enough. So please enjoy and sorry again for the super late chapter.**

* * *

"Thank you for the help Nai-kun," Yogi said as he walked over to the two young men. Nai and Gareki separated at his approach and Nai smiled brightly as Gareki looked over to where the ground was charred from the vaporized varuga.

"Man, I need more practice. I can't believe I got scratched by such an easy one," Gareki muttered to himself as Tsukumo joined the three men.

"I wouldn't have called this an easy one Gareki-kun," Tsukumo said as she smiled lightly at the group. "This one was two times the normal strength of a varuga. And, to top it off, it was a variant we'd never dealt with before. You did fine. The real question here is are you okay? You took quite the hit earlier."

"Just a small scratch. Nothing much to worry about," Gareki said as he turned his attention back to the group and showed them a shallow scratch about 5 inches long. "It just hurt like hell when it scratched me. You heard me scream Nai?"

The young man nodded his head and looked down at Gareki's arm in concern. He then took the arm into his hands and applied a healing force to the wound. The three Circus members watched in shock as the wound disappeared completely.

"Since when could you do that?" Gareki asked seriously.

"I don't know," was Nai's response before he smiled widely and pulled Gareki and Tsukumo by the arms over to the portal. The three circus members looked at each other seriously before following Nai over to the portal. As soon as they entered the ship they were greeted by an irate Hirato and the captain of the first ship, Tsukitachi, smiling his usual smile.

"Welcome back," stated Tsukitachi as Hirato waltzed over to the group.

"Nai, why did you do that?" Hirato asked none too calmly as he stared deep into Nai's eyes, anger clear in his own.

"Gareki got hurt," was all Nai said as he tried to walk past Hirato into the ship's interior. Hirato wasn't having any of that and grabbed the young man by the arm. Still holding Nai's arm, Hirato moved into the ship himself and took the young man straight into the infirmary. He then threw Nai onto one of the empty beds while everyone crowded into the room with concern.

"Hirato wha-"

Tsukumo was cut off by a wave of the man's hand as he looked back at the crowd behind him.

"Nai here just broke down the door to his room. Can anyone tell me how he got so strong in such a short amount of time?"

The room went silent at Hirato's claim as Doctor Akari walked into the room.

"The most I can guess at is that his enhanced strength is due to some kind of change in his environment," Akari stated as he walked over and stood next to Nai. "Anything else new come up?"

"...Just now, Nai healed my cut with some kind of power after I got scratched by a varuga not even 15 minutes ago," Gareki said carefully. Hirato stiffened as Tsukitachi's smiling mask broke into a grimace. Akari's eyes widened at the mention of such a power and began to examine Nai carefully. After checking all of the basics and finding nothing odd he started a series of tests where he asked Nai to do feats of strength. To everyone's shock Nai was able to lift the hospital bed with one hand and was also able to lift a particularly heavy piece of equipment without much exertion.

"Nai, do you feel okay?" Akari asked after a few minutes of contemplation.

"...I feel hot," Nai said shyly as he moved to hide behind Gareki.

"Hot?! Oh no. Oh no no no no no no no. This shouldn't even happen, he's humanoid after all. But what else is there t-"

"Spit it out Akari. What's wrong with Nai?!" Gareki asked anxiously as he stared deep into the doctor's eyes.

"Nai is, to put it frankly, he is in heat."

"...Whaaaaaaaaaaat?!" everyone said simultaneously as they all turned to stare at Nai.

"That explains why he's clingier than usual. And he snapped at Tsukumo-chan earlier today too," Yogi stated as Tsukumo nodded and Gareki turned his head to try to get a better look at Nai. Nai just looked up at Gareki in confusion, eaking a small smile out of the dark haired youth. Turning back to Akari,

"So what do we have to do while he's in this state?"

"...Uh you may not like this but..."

"Well come on. Spit it out," Gareki said in annoyance.

"...When his heat is at it's highest point he will need some sort of release...and that usually means sex," Akari stated uncomfortably as he rubbed the back of his neck.

"...Is that all then?"

"No...his heat will last for a few days so he will need help during those days. I'm not going to force you Gareki-kun, but since Nai is so set on you..."

*sigh~*"Alright. I'll help him out. How often do you think these heats will happen?"

"I honestly don't know when they will occur after this one but once we can establish a schedule then there shouldn't be anymore problems."

"Well that's all fine and good, but what am I supposed to do without two of my fighters?" Hirato asked frankly. All attention shot to the third's captain just before Tsukitachi's smile returned and Akari glared at him.

"I could loan you a couple of members since we received some new recruits recently as well. How about Jiki and Kiichi?" the first's captain offered politely.

"That's fine. I just want them here in an hour and no less," Hirato said in clear irritation, his usual fake smile tainted with malice. Everyone in the room shuddered except for the two men who knew him best. Tsukitachi left without much effort as Akari walked over and sat down on the bed.

"I have to talk to Gareki-kun alone if you don't mind clearing out?"

Everyone looked at the young man before clearing out and leaving Akari alone with Gareki and Nai.

"I have some items for you that will help you during this whole fiasco. You'll find them already in your room with detailed instructions on what to do. But understand one thing Gareki...Nai will not be the one to do the penetrating."

"Eh?"

"Simply put, Nai is too docile to do anything other than to take you into himself. Understand?"

"...I understand," Gareki said lightly as he turned around and picked Nai up. The younger man didn't think much of it and snuggled closer to Gareki in response. Gareki smiled lightly at the younger man before turning about and going out the door to go to their room. Akari sat in silence for a bit, contemplating the things to come.

"...I hope both of them can find happiness," Akari said quietly as he stood to go back to the portal and take his shuttle back to his lab.

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 **Super mondo big thank you to all of you wonderful people who've been sticking around for this story for so long and thank you blackkyu, ponpo, Z, and for the awesome reviews. I love hearing feed back from my readers and this really helps me become a better writer. Please be open with me as I take criticism very seriously lol.**

 **And thank you rasclieboobear for your insight. I understand that this time around Nai may seem very OC, but there is a reason for it which is answered in this chapter lol. Hope this cleared things up a bit.**

 **And again I am so sorry for taking so long to put this chapter out. So glad the summer is finally over and I can get back to this a bit more often. So hope you guys enjoyed this chapter and please let me know if you'd like to see anything change for this story. See y'all in the next chapter. Ja ne(bye)! (^-^)/))**


	3. Chapter 3

**What's up everybody! It's been a while. I know I said I would have more time to do this kind of thing, but sorry, that turned out to be a lie. I apologize profusely for not having this chapter out earlier. It is again school and work that kick my ass repeatedly. I also am going into the Navy possibly so in that case I may take a massive break from writing for a few years. Just a warning now. Anyways we are at the finale for this piece and yes, when compared to my other stories, this is rather short. But such is life. Thanks for sticking around for so long guys and I hope you enjoy this last chapter of Spring Fever. Read on!**

* * *

As Gareki walked down the hallway, a very cuddly Nai in his arms, he ran into Yogi and Tsukumo waiting outside of their bedroom door.

"Yogi, Tsukumo, please move aside," Gareki said blandly as he moved to go past them. However, Yogi wasn't in the most hospitable of moods, and blocked Gareki's way.

"You will listen to what we have to say Gareki-kun, whether you like it or not."

*sigh~* "Fine but make it quick. Nai's heat could start any minute now."

"About this whole sex thing, how are you intending to do it?"

"Hah?!"

"Nai is a male and all. So he's the one who's going to to-"

"Idiot! Nai's way too docile to do anything but take it. I'm the one on top not him," the raven haired boy replied crossly as he shoved his way into the room. One look around was all it took to see that everything had been provided for them. Turning back to the two concerned Circus members, "We won't be coming out very often for the next few days. Try not to open the door if you can avoid it."

With that, Gareki slammed the door shut and locked it from the inside, leaving a very stunned Yogi and Tsukumo to turn around and go into the main foyer. The two sat down, still in shock as their captain came in and clapped his hands for their attention. Snapping out of their daze, they looked up at Hirato expecting to be berated.

"And so it's begun," was all Hirato said as the two members from the First ship came in and bowed in introduction. _I hope they'll be ok_ , Yogi thought as he stood to greet their temporary members.

* * *

Upon closer inspection on the room, Gareki noticed that the usual bunk beds had been replaced with a double bed. In one corner he saw a fridge no doubt full of food and water and a microwave on top of it. on a table in the other corner he saw a book that hadn't been there earlier and another thicker book under that. Setting Nai down on the bed gently, he turned to grab the top book when Nai tugged at his sleeve. The raven haired man looked back at the boy as Nai gazed up at him petulantly, his eyes begging him not to go.

"It's ok Nai. I'm just gonna grab the books over on that table," Gareki said as he gently removed the younger man's hand from his sleeve. Nai waited as the older man walked over and grabbed the books before he turned around and sat on the bed. The top, thinner book was an instruction manual for Gareki and the bottom one was something new to read while Nai was knocked out due to periods of exhaustion, as the book explained. Gareki read the entire book through silently as Nai laid his head on the man's lap, eyes closed in contentment.

 _...Loosen the opening with saliva coated fingers or lube if they have any. Massage the area as you play with the front then..._ Gareki was just finishing up as he felt Nai stir from his spot. When the man looked up, Nai was flushed from head to toe and was clumsily trying to remove his clothes.

"Hot," was all Nai said as he continued to struggle with the garments. Gareki smiled lightly before he closed the book with a snap and set on top of the thicker one on the ground. He moved over towards Nai, careful not to startle the young humanoid. Nai noticed Gareki coming closer and started to inch away slowly until his back hit the wall. After that the boy looked down shyly, shirt half undone, eyes clouded over with obvious desire. Gareki almost had to do a double take and swallowed nervously as he came closer to the white haired younger man.

"Nai, I'm gonna help you now ok? You don't have to be scared, alright," the raven haired man said lightly as he started to undress Nai. The younger man just shivered silently as his shirt was stripped away. Gareki then slowly caressed Nai's torso, the light gesture causing the boy to gasp as heat coursed through his body. The older man soon moved his head in to kiss the younger lightly on the lips. As he deepened the kiss, Nai began to moan against him and Gareki found his hands naturally moving lower until they were stripping off the rest of the young man's clothes.

He then began to gently stroke Nai's slightly inflamed cock. The boy moaned even louder as waves of pleasure rolled off of his skin. Gareki soon found himself removing his own clothes. He wasn't fast enough for Nai though, as the white haired boy unzipped Gareki's pants and took the older man's cock into his mouth. Gareki flinched at the feeling of his dick being swallowed by Nai, before he lost himself to the younger man's tongue work. Gareki pulled Nai off before he could cum and pushed him back onto the soft pillows. He once again stroked the boy's cock as he coated his fingers and inserted the first one into Nai's hole. Nai's hips bucked forward upon being entered for the first time, the sensation slowly driving his mind higher and higher.

The boy's moans reached fever pitch as Gareki continued to work the opening, as he made Nai wriggle and gasp underneath him.

"Gare_ki," the white haired boy moaned as the third finger was added to his opening. Soon enough Nai was loose enough for the raven haired man to insert his own flaming cock. Upon being entered Nai wrapped his arms around Gareki's neck and clung tightly to the older man, trying to stave off the huge wave of heat that'd just entered him.

"Gareki_love_you," was all the boy could get out before Gareki began to move inside of him. Once he got going Gareki was like an unleashed horse, driving his cock in and out of the younger man as he continued to moan beneath him. _Weird. I've never felt like this_ , the raven haired man thought as his pace reached breaking point. Nai, finding himself faced with such a fierce amount of pleasure, came as he squeezed tightly around Gareki, causing him to cum as well. The two stayed linked together for a moment more before the older man pulled out of Nai as the boy continued to hang on to him. Gareki knew that Nai was going to fall asleep in just a few moments, so he decided to pull the young man close to his side and to take a nap with him.

The process repeated many times over the course of four days and nights, as the third ship became more and more anxious about the couple behind the closed door.

"I hope they're ok," Yogi kept saying as he did his 30th round of pacing for the day.

"Relax Yogi. They're just fine, I'm sure," Tsukumo said in an attempt to calm the man down. At last Gareki and Nai came out of their room, Gareki cradling Nai in his arms on their way to the bath room to get cleaned up. The entire third ship heaved a huge sigh of relief, as many smiles broke on most of the faces of the team.

"So nice to see them up and about," Hirato said with his usual fake smile as he walked into the main foyer.

"Yay! We need to have a big party to celebrate their retu-"

Yogi was cut off as a book came flying at him and hit him square in the face.

"That's enough out of you," was all Hirato said as he turned to go back to the library.

"What was that for Hirato-san?!" Yogi called after him, hurt at his cold attitude.

"They won't want to celebrate. They'll want to relax and sleep, Yogi," Tsukumo stated blandly as she waltzed off to her own room. Yogi just sat on the floor like the confused man he was until on of the first ship's fighters came into the room and pulled him onto a couch. He was then left to his own devices.

 _IDIOT_ , everyone on the ship thought, except for a peacefully sleeping Nai and Gareki.

* * *

"Nai hurry up!" Gareki called as he ran towards the portal.

"Coming!" the young boy shouted back as he ran along cheerfully after his beloved. The two were transported onto the battle scene and proceeded to kick butt like always before heading back onto the ship. They were greeted by a very cross Akari and a fake smiling Hirato.

"Akari, what's up?" Gareki asked after he gave the lambs the usual greeting.

"I came to check on Nai's condition. Now that we've established his cycles I need to make sure I keep up on his health and any new abilities that may pop up. Not like I have a choice," the doctor griped as he walked further into the ship, Nai following closely behind.

"Who would've thought that you two would become so lovey dovey," Tsukitachi called from the foyer as the team filed in.

"Tsukitachi," was all the raven haired man said in greeting as he sat on the couch farthest from the man.

"But to think that the boy's heats would be every six months, that was shocking news to hear," the man replied unperturbed by Gareki's cold attitude.

"That's how it is. If you'll excuse me."

Gareki got up and went into the infirmary wing as the rest all chuckled lightly.

"Gareki!" Nai called out happily as he dashed down the hall towards him. Akari followed behind him with a very tired expression.

"I found nothing wrong," was all he reported before continuing on his way. Nai and Gareki embraced before heading to their room to spend the rest of their evening in peace. And with peace comes (^_-).

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 **And so ends yet another story. Another shall soon be posted once I get time. Hope you guys enjoyed this unique spin on Nai and Gareki's relationship and I look forward to seeing y'all in my next story. So until next time, arigatou gozaiimasu(thank you very much)! *bows***


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